Use a wrapper type implementing Sync, instead of static mut

`static mut` is generally best avoided. It seems to only be necessary
currently to allow the use of non-`Sync` types, since pointers are not
sync.

This also removes the `NULLPTR` constant in favor of using
`std::ptr::null`, uses `.as_ptr()` instead of casting, and uses the
arrray repeating syntax to define `types_null`. None of those should
impact behavior or the public API.

`*_requests` and `*_events` static are no longer public now. This is
theoretically a breaking change, but shouldn't really impact anything.

wayland-scanner/src/c_interfaces.rs

@@ -1,5 +1,4 @@
 use std::cmp;
-use std::iter::repeat;
 
 use proc_macro2::{Literal, TokenStream};
 use quote::{format_ident, quote};
@@ -27,14 +26,13 @@ pub(crate) fn generate_interfaces_prefix(protocol: &Protocol) -> TokenStream {
 
  let types_null_len = Literal::usize_unsuffixed(longest_nulls);
 
- let nulls = repeat(quote! { NULLPTR as *const wayland_backend::protocol::wl_interface })
- .take(longest_nulls);
-
  quote! {
- const NULLPTR: *const std::os::raw::c_void = 0 as *const std::os::raw::c_void;
- static mut types_null: [*const wayland_backend::protocol::wl_interface; #types_null_len] = [
- #(#nulls,)*
- ];
+ use std::ptr::null;
+ struct SyncWrapper<T>(T);
+ unsafe impl<T> Sync for SyncWrapper<T> {}
+ static types_null: SyncWrapper<[*const wayland_backend::protocol::wl_interface; #types_null_len]> = SyncWrapper([
+ null::<wayland_backend::protocol::wl_interface>(); #types_null_len
+ ]);
  }
 }
 
@@ -47,24 +45,24 @@ pub(crate) fn generate_interface(interface: &Interface) -> TokenStream {
  let version_value = Literal::i32_unsuffixed(interface.version as i32);
  let request_count_value = Literal::i32_unsuffixed(interface.requests.len() as i32);
  let requests_value = if interface.requests.is_empty() {
- quote! { NULLPTR as *const wayland_backend::protocol::wl_message }
+ quote! { null::<wayland_backend::protocol::wl_message>() }
  } else {
  let requests_ident = format_ident!("{}_requests", interface.name);
- quote! { unsafe { &#requests_ident as *const _ } }
+ quote! { #requests_ident.0.as_ptr() }
  };
  let event_count_value = Literal::i32_unsuffixed(interface.events.len() as i32);
  let events_value = if interface.events.is_empty() {
- quote! { NULLPTR as *const wayland_backend::protocol::wl_message }
+ quote! { null::<wayland_backend::protocol::wl_message>() }
  } else {
  let events_ident = format_ident!("{}_events", interface.name);
- quote! { unsafe { &#events_ident as *const _ } }
+ quote! { #events_ident.0.as_ptr() }
  };
 
  quote! {
  #requests
  #events
 
- pub static mut #interface_ident: wayland_backend::protocol::wl_interface = wayland_backend::protocol::wl_interface {
+ pub static #interface_ident: wayland_backend::protocol::wl_interface = wayland_backend::protocol::wl_interface {
  name: #name_value as *const u8 as *const std::os::raw::c_char,
  version: #version_value,
  request_count: #request_count_value,
@@ -89,15 +87,15 @@ fn gen_messages(interface: &Interface, messages: &[Message], which: &str) -> Tok
  let array_values = msg.args.iter().map(|arg| match (arg.typ, &arg.interface) {
  (Type::Object, &Some(ref inter)) | (Type::NewId, &Some(ref inter)) => {
  let interface_ident =format_ident!("{}_interface", inter);
- quote! { unsafe { &#interface_ident as *const wayland_backend::protocol::wl_interface } }
+ quote! { &#interface_ident as *const wayland_backend::protocol::wl_interface }
  }
- _ => quote! { NULLPTR as *const wayland_backend::protocol::wl_interface },
+ _ => quote! { null::<wayland_backend::protocol::wl_interface>() },
  });
 
  Some(quote! {
- static mut #array_ident: [*const wayland_backend::protocol::wl_interface; #array_len] = [
+ static #array_ident: SyncWrapper<[*const wayland_backend::protocol::wl_interface; #array_len]> = SyncWrapper([
  #(#array_values,)*
- ];
+ ]);
  })
  }
  });
@@ -118,17 +116,17 @@ fn gen_messages(interface: &Interface, messages: &[Message], which: &str) -> Tok
  wayland_backend::protocol::wl_message {
  name: #name_value as *const u8 as *const std::os::raw::c_char,
  signature: #signature_value as *const u8 as *const std::os::raw::c_char,
- types: unsafe { &#types_ident as *const _ },
+ types: #types_ident.0.as_ptr(),
  }
  }
  });
 
  quote! {
  #(#types_arrays)*
 
- pub static mut #message_array_ident: [wayland_backend::protocol::wl_message; #message_array_len] = [
+ static #message_array_ident: SyncWrapper<[wayland_backend::protocol::wl_message; #message_array_len]> = SyncWrapper([
  #(#message_array_values,)*
- ];
+ ]);
  }
 }